A blacklist (also called a blocklist) is a curated database of websites, apps, domains, or sources that an advertiser or platform has flagged to exclude from a campaign — typically because they are associated with fraud, spam, low quality, inappropriate content, or poor performance. In programmatic advertising, blacklists are a primary tool for brand safety and budget protection, ensuring ads never appear in environments that could waste spend or damage the brand.
 

When an advertiser applies a blacklist, the DSP filters out any impression originating from a listed source before bidding. This pre-bid exclusion prevents the advertiser from ever paying to appear on flagged inventory. Blacklists can target specific domains, app bundle IDs, content categories, or even particular placements within a site. Many advertisers maintain evolving blacklists, adding sources as verification data reveals fraud, invalid traffic, unsafe adjacency, or chronic underperformance.
 

Blacklists are the conceptual opposite of whitelists (allowlists). A blacklist says "run everywhere except these blocked sources," maximizing reach while screening out known bad actors. A whitelist says "run only on these approved sources," maximizing control and safety at the cost of scale. Advertisers choose between — or combine — these approaches based on campaign goals: brand campaigns with strict safety requirements may lean on whitelists, while performance campaigns chasing scale often rely on blacklists to stay broad while avoiding the worst inventory.
 

For brand safety, blacklists help advertisers avoid content categories like hate speech, violence, adult material, misinformation, or anything misaligned with brand values. A single ad placed next to objectionable content can trigger public backlash, so proactive blocking is essential for risk management. Industry tools and verification vendors supply continually updated category-based and domain-based blacklists that advertisers can adopt and customize.
 

For fraud prevention, blacklists exclude domains and apps known for bot traffic, domain spoofing, ad stacking, or other invalid-traffic schemes. Because fraudsters constantly create new properties, effective blacklists must be dynamic, informed by real-time detection rather than static lists that quickly go stale.
 

Publishers care about blacklists too. Being placed on widely used blacklists — through invalid traffic, unsafe content, or quality issues — cuts a publisher off from demand and revenue. This gives publishers a strong incentive to maintain clean traffic, safe content, and transparent supply paths. Used well, blacklists are a precise, scalable defense that keeps programmatic budgets working in trustworthy environments rather than leaking into fraud or reputational risk.